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HALLUCINATIONS

Hallucinations are abnormal sensory perceptions of

stimuli that occur in the absence of external stimuli.

Hallucinations can be visual, auditory, tactile, olfac-

tory, or gustatory. There are numerous disorders that

are associated with hallucinations, including, but not

limited to, schizophrenia, posttraumatic stress disor-

der (PTSD), substance use and withdrawal, and mood

disorders. To determine appropriate treatment, the eti-

ology of the hallucinations must be ascertained by

conducting a thorough medical history, psychological

assessment, and, if warranted, imaging studies.

Definition

Hallucinations can be defined as conscious abnormal

sensory perceptions that do not have a source in the out-

side world. Hallucinations can involve one or more

senses, including visual, auditory, gustatory, olfactory,

or tactile. People who experience hallucinations report

experiences such as seeing things that aren’t there,

hearing voices that no one else can hear, feeling that

there is something crawling on their skin, smelling

things that no one else can smell, or tasting things that

other people cannot taste.

In one study, Johns and colleagues found that preva-

lence of hallucinations in a community sample ranged

from 2% to 10%. There is currently no evidence that

hallucinations occur more frequently in some racial or

ethnic groups than in others, and gender does not appear

to affect the presence or frequency of hallucinations.

Disorders Associated

With Hallucinations

Hallucinations are associated with numerous disor-

ders, illnesses, and states. Currently, there does not

appear to be a single underlying cause that can explain

all types of hallucinations. Several explanations and

hypotheses have been put forth for various disorders,

but to date, the causes of hallucinations are not com-

pletely understood.

Hallucinations are most commonly associated with

schizophrenia, a mental illness characterized by disor-

dered perceptions, thoughts, and behaviors. According

to the National Institute of Mental Health, approxi-

mately 75% of individuals with a diagnosis of schizo-

phrenia experience auditory hallucinations, visual

hallucinations, or both. The auditory hallucinations may

be command hallucinations, in which the person hears

voices ordering him or her to do something.

Other disorders are that are less frequently associated

with hallucinations include eye disorders such as macu-

lar degeneration or glaucoma; high fever, particularly in

children and the elderly; late-stage Alzheimer’s disease;

migraine headaches; intoxication or withdrawal from

alcohol or drugs; severe medical illness such as liver or

kidney failure or brain cancer; severe mood disorders

such as bipolar disorder and depression; post traumatic

stress disorder; and temporal lobe epilepsy. In addition,

hallucinations are also associated with normal sleep-

wake cycles. Approximately one third of adults experi-

ence hypnagogic hallucinations, which occur as a

person passes from wakefulness into sleep; another 10%

to 12% of adults report hypnopompic hallucinations,

which occur as the person is waking up.

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